DBIx::Class::DeploymentHandler::Manual::Intro(3pm)

NAME
DBIx::Class::DeploymentHandler::Manual::Intro - Introduction to DBIx::Class::DeploymentHandler

Why is DBIx::Class::DeploymentHandler worth using?
The most obvious reasons for using DBIx::Class::DeploymentHandler are that it can run multiple SQL scripts as well as Perl scripts, unlike DBIx::Class::Schema::Versioned, which only allows for a single SQL script. It is also extremely extensible, and is an opportunity for a break from backwards compatibility, so some regrettable decisions are avoided.

Sample database
Follow DBIx::Class::Manual::Intro except for the parts setting up the database. After you are done, You should have the following files.

 MyDatabase/
 |-- Main
 |   |-- Result
 |   |   |-- Artist.pm
 |   |   |-- Cd.pm
 |   |   `-- Track.pm
 |   `-- ResultSet
 `-- Main.pm

Add a line like the following in your MyDatabase::Main file:

 our $VERSION = 1;

or if you are using a newer Perl you can use the prettier syntax:

 package MyDatabase::Main 1;

By default DBIx::Class::DeploymentHandler only uses integers for versions, this makes versioning much simpler for figuring out what version is next (or previous.) However, if you are using decimal numbers for versioning, you will need to create a separate DeploymentHandler class, as per DBIx::Class::DeploymentHandler::Cookbook::CustomResultSource, and set the VersionHandler class_name from Monotonic to ExplicitVersions or DatabaseToSchemaVersions, as these handle version numbers as strings instead of integers.

install.pl
Our first script, "install.pl" reads our schema file and creates the tables in the database.

 #!/usr/bin/env perl

 use strict;
 use warnings;
 use aliased 'DBIx::Class::DeploymentHandler' => 'DH';
 use Getopt::Long;
 use FindBin;
 use lib "$FindBin::Bin/../lib";
 use MyDatabase::Main;

 my $force_overwrite = 0;

 unless ( GetOptions( 'force_overwrite!' => \$force_overwrite ) ) {
     die "Invalid options";
 }

 my $schema = MyDatabase::Main->connect('dbi:SQLite:mydb.db');

 my $dh = DH->new(
     {
         schema              => $schema,
         script_directory    => "$FindBin::Bin/../dbicdh",
         databases           => 'SQLite',
         sql_translator_args => { add_drop_table => 0 },
         force_overwrite     => $force_overwrite,
     }
 );

 $dh->prepare_install;
 $dh->install;

  dbicdh - Our migration scripts
Running "install.pl" should create the following:

 dbicdh/
 |-- SQLite
 |   `-- deploy
 |       `-- 1
 |           `-- 001-auto.sql
 `-- _source
     `-- deploy
         `-- 1
             `-- 001-auto.yml

You may wish to turn on debug logging before running this script by setting the environment variable "DBICDH_TRACE" to 1.

001-auto.sql

DBIx::Class::DeploymentHandler automatically generates SQL from our schema that is suitable for SQLite

001-auto.yml

This contains all of the raw information about our schema that is then translated into the sql.

Population

To truly take advantage of all DBIx::Class::DeploymentHandler offers, you should probably be using it for population. To do that all you need to do is create a file called "dbicdh/_common/deploy/1/create_artists.pl":

  sub {
     my $schema = shift;
     $schema->resultset('Artist')->populate([
        ['artistid', 'name'],
        [1,          'Marillion'],
        [2,          'The Moutain Goats'],
        [3,          'Ladyhawke'],
     ]);
  };

Upgrading
Add a line to MyDatabase/Main/Result/Cd.pm below

 __PACKAGE__->add_columns(qw/ cdid artist title /);

with

 __PACKAGE__->add_column(isbn => { is_nullable => 1 });

Aside: It must be nullable or have a default - otherwise the upgrade will fail for logical reasons. To be clear, if you add a column to a database and it is not nullable and has no default, what will the existing rows contain for that column?

Now you need to modify the schema version in your MyDatabase::Main file to tell DBIx::Class::DeploymentHandler the new schema version number. You will want to remember the earlier advice about integer version numbers.

 our $VERSION = 2;

So here is our next script, "upgrade.pl":

 #!/usr/bin/env perl
 use strict;
 use warnings;
 use aliased 'DBIx::Class::DeploymentHandler' => 'DH';
 use FindBin;
 use lib "$FindBin::Bin/../lib";
 use MyDatabase::Main;
 my $schema = MyDatabase::Main->connect('dbi:SQLite:mydb');

 my $dh = DH->new({
    schema              => $schema,
    script_directory    => "$FindBin::Bin/../dbicdh",
    databases           => 'SQLite',
    sql_translator_args => { add_drop_table => 0 },
 });

 $dh->prepare_deploy;
 $dh->prepare_upgrade({ from_version => 1, to_version => 2});
 $dh->upgrade;

Our script directory now looks like:

  dbicdh/
  |-- SQLite
  |   |-- deploy
  |   |   |-- 1
  |   |   |   `-- 001-auto.sql
  |   |   `-- 2
  |   |       `-- 001-auto.sql
  |   `-- upgrade
  |       `-- 1-2
  |           `-- 001-auto.sql
  `-- _source
      `-- deploy
          |-- 1
          |   `-- 001-auto.yml
          `-- 2
              `-- 001-auto.yml

The new "deploy/001-auto.sql" and "deploy/001-auto.yml" files are the state of the db as at that version. The "upgrade/1-2/001-auto.sql" file is the most interesting one; it is what gets your database from version 1 to 2.

And again, you can create a Perl file like we did previously with the deploy stage.

AUTHOR
Arthur Axel "fREW" Schmidt <frioux+cpan@gmail.com>

COPYRIGHT AND LICENSE
This software is copyright (c) 2025 by Arthur Axel "fREW" Schmidt.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.